The present invention relates to transducer head assemblies for magnetic recording on disc drives, and more particularly to self-loading negative pressure air bearing sliders.
Transducer head assemblies that "fly" relative to a rotating disc are used extensively in rotating disc drives. The assemblies include an air bearing slider for carrying a magnetic transducer proximate the rotating disc. A track accessing arm positions the slider and transducer over individual data tracks on the disc surface.
A gimbal is positioned between the slider and the track accessing arm to provide a resilient connection that allows the slider to follow the topography of the disc. The gimbal includes a dimple that is in point contact with the slider. The dimple provides a point about which the slider can pitch and roll while following the topography of the disc.
A self-loading, negative pressure air bearing slider (NPAB) includes a pair of side rails positioned along its side edges and disposed about a recessed area to form a pair of air bearing surfaces. A cross rail extends between the side rails and is positioned near the slider's leading edge.
As the disc rotates, the disc drags air under the slider and along the air bearing surfaces in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the side rails, the skin friction on the air bearing surfaces causes the air pressure between the disc and the air bearing surfaces to increase which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface.
The cross rail forms a negative pressure cavity trailing the cross rail, between the side rails. The negative pressure cavity is typically 5 to 10 microns deep. The air expands in this cavity with a consequent decrease in pressure. The pressure in the cavity may become subambient, in which case the integral of pressure over the cavity area provides a self-loading force on the slider which forces the slider toward the disc surface. The self-loading force counteracts the hydrodynamic lifting force developed along the side rails. The counter action between positive and negative forces on the slider reduces flying height sensitivity with respect to disc velocity and increases air bearing stiffness.
The disc tangential velocity is greater at its outer diameter than at its inner diameter. The magnitude of the positive pressure developed along the side rails increases with the sliding velocity. However, the magnitude of the self-loading force also increases with the sliding velocity. The increasing self-loading force prevents the increasing positive pressure from forcing the slider away from the disc. Therefore, the equilibrium clearance of the self-loading air bearing slider is less dependent on sliding velocity than a conventional air bearing slider.
The self-loading air bearing slider is also stiffer than the conventional air bearing slider. This effect is due to relatively large surface areas that are required to support the slider at a specified clearance. The surface area of the self-loading bearing must be larger than that of a conventional bearing, to provide adequate lifting force to resist the self-loading force as well as the spring preload applied by the track accessing arm.
Further, the self-loading air bearing slider is less sensitive to altitude than the conventional air bearing slider. When the ambient pressure is reduced by operating the disc drive at an altitude high above sea level, the effects on the positive and negative pressures are similar and tend to cancel each other. Thus, the self-loading air bearing clearance decreases less than a similar conventional air bearing clearance.
It has been found that the advantages of the self-loading bearing are maximized by making the negative pressure cavity area as large as possible. Warner et al. U.S. Pat. No. 4,475,135 disclose a self-loading magnetic head air bearing slider having a pair of side rails and a cross rail which is positioned at its leading edge. The cross rail lies in a plane defined by the side edges and includes a full width taper at the leading edge. The full width taper provides a faster liftoff from the disc surface.
Although the slider disclosed by Warner et al. maximizes the area of the negative pressure cavity, it also has undesirable features. First, the full width leading edge tends to collect wear particles and similar debris. This debris sheds occasionally and is dragged between the slider and the disc, causing increased wear to both the air bearing surface and the disc surface. Second, the cross rail and the leading edge taper cause the slider to fly with an unusually high pitch angle. A very high pitch angle degrades the stiffness of the air bearing.